Process and apparatus for production of vinyl chloride monomer

ABSTRACT

Process and apparatus to form vinyl chloride monomer from ethylene dichloride in a cracking furnace, including a firebox chamber having a thermal protective layer disposed on refractory walls and/or process tubes disposed within the chamber, a quencher to form vinyl chloride monomer, and fractionator separate products. The thermal protective layer which contains an inorganic adhesive for metal/alloy tubes or colloidal silica and/or colloidal alumina for refractory walls or ceramic tubes, a filler, and one or more emissivity agents.

BACKGROUND OF INVENTION

In the production of vinyl chloride monomer, pyrolysis furnaces, alsoknown as cracking furnaces, are used to crack ethylene dichloride (EDC)in the presence of catalysts in the process to form vinyl chloridemonomer (VCM), known as chloroethene in IUPAC nomenclature, toultimately produce polyvinyl chloride (PVC). Cracking the EDC in acontinuous feed production process is the predominant process for makingVCM. In the production process, chlorine is reacted with ethylene toproduce EDC, which is further cracked to form VCM and the byproducthydrochloric acid. Oxygen may optionally be added to the processresulting in the additional byproduct of water. The hydrochloric acidmay further be fed back into the process as a source of chlorine. PVC isthen produced by polymerizing the VCM, removing excess VCM, and dryingthe product. The VCM is polymerized in a batch reactor to produce PVC.Excess VCM is then removed and the PVC is dried. The dried PVC may bepackaged and stored to be delivered for further manufacturing processes.

Almost all VCM produced is used to manufacture PVC resins. The PVC isused in a large variety of end products including consumer products,packaging, and construction. Vaporized EDC is dried and passed over acatalyst packed in stainless steel tubes that are directly heated in acracking furnace. The hot effluent gases are quenched and the condensedgases fed into a fractionating tower operating under pressure. Theproduct VCM is formed by condensing the overhead vapors in a watercondenser. The VCM is then filtered and sent to either a storage tankfor further processing to produce PVC or sold to other manufacturersthat make PVC.

Each cracking furnace has a refractory lined firebox containing amultiplicity of high alloy metal or ceramic cracking lines, composed ofprocess pipes, through the interior passages of which flows the EDCfeedstock to be cracked. Various catalysts may be added to the EDCfeedstock including oxygen, recycled hydrogen chloride, and other wellknown catalysts. Refractories used to line the firebox are classified asbasic, high aluminum, silica, fireclay and insulating. Specialrefractories include silicon carbide graphite, zircon, zirconia, andfused cast, among others. Refractory lining may be formed of bricks,castables, or thermal ceramic fiber to cover the interior of thefirebox. A suitable amount of diluting steam may be included in theprocess. Burners are located on the floor and/or walls of the firebox toprovide the heat necessary. The heat transfers through themetallic/ceramic materials of the reaction lines into the hydrocarbonfeedstock that flows within the reaction lines. Known metallic crackinglines may be as long as 2000 feet and may be coiled in a serpentineshape that runs vertically up and down in the firebox or it may be asshort as 40 feet in a straight single pass through the firebox.

The process tubes are heated using convection heating or a combinationof convection and radiant heat. The tube may be made of a metal alloy orceramic. Alloys include most stainless steel, cast alloys, wroughtalloys, carbon steel and the like, which are well known to those skilledin the art. The refractory materials, both hard and ceramic fiber,incorporated into the firebox contain the heat permitting the processtubes to be heated for the cracking or related reactions to occur. Thefireboxes themselves can deliver an increased radiant heat load to theprocess tubes.

Traditional process tubes are fabricated from cast or wrought, highalloy stainless steels. Coke layers form along the inner surfaces of theprocess tubes during normal operation resulting in reduced mass flowthrough the tube and a reduction in heat transfer through the sides ofthe tubes. Additional formation of metal carbides along the tube walls,referred to as carburization, further reduces the structural life of thefurnace tubes. The furnace must be periodically shut down in order toremove the deposits of coke. This factor results in a substantial lossof production and facility downtime. Furthermore, coke is an excellentthermal insulator requiring higher temperatures resulting in higher fuelcosts and shorter tube life.

Process tubes resistant to coking and carburization are desirable.Efforts to produce such resistant process tubes have concentrated ondeveloping a variety of new alloys that are resistant to carburizationand reduce the development of coke layers. Some of these efforts haveconcentrated on layering different alloys on the tubes. Research hasshown that, like aluminides, aluminum and silicon containing alloys,iron, chrome, and certain other alloys also prevent coking andcarburization. Ceramic and alloys containing silicon have also beenfound potentially useful.

The use of a coating film to inhibit coke formation in an ethylenedichloride to a vinyl chloride monomer pyrolysis cracker is known. U.S.Pat. No. 7,132,577 and U.S. Patent Application Publication No.2006/127,700 by Jo et al., published on Nov. 7, 2006 and Jun. 15, 2006respectively, disclose a coating film for inhibiting coke formation inan ethylene dichloride pyrolysis cracker and a method of producing thecoating film. Specifically, the invention of Jo et al. teachesinhibiting coke formation by coating a boron compound on a heat-transfersurface of the cracker, resulting in a 50% or greater reduction in cokeformation. The coating film appears to have been applied solely to theinternal surface of the process tubes. Specifically, the inner surfaceof the process tubes are coated with the boron compound composition. Theethylene chloride conversion and the selectivity to a vinyl chloridemonomer during the pyrolysis reaction are not affected by the reductionin coke formation.

Similarly, U.S. Pat. Nos. 6,368,494 and 6,454,995 issued to Tong, onApr. 9, 2002 and Sep. 24, 2002 respectively, teaches a method forreducing coke in an EDC-VCM furnaces by exposing the heat transfersurfaces to a phosphite compound. The phosphite compound either alone orin combination with a carrier is applied to the inner surface of theprocess tubes by feeding the phosphite compounds through the tubeseither prior to or contemporaneous with the EDC feedstock. The phosphitecompounds are fed through the process tubes, which are exposed to thestream for thirty minutes to two days.

U.S. Pat. No. 6,228,253 issued to Gandman on May 8, 2001 discloses amethod for removing and suppressing coke formation during pyrolysis bycutting off the feedstock to one or more coils (process tubes) andadding a decoking additive to the steam flow comprised of a group IA/IIAmetal salt, which coats the coils inner surface with a “glass layer”that inhibits coke formation.

U.S. Pat. No. 6,830,676 issued on Dec. 14, 2004 and assigned toChrysalis Technologies Incorporated teaches coking and carburizationresistant iron aluminides for hydrocarbon cracking. In this invention,the cracking tubes have a lining of iron aluminide alloy which isfouling and corrosion resistant. U.S. Patent Application No.2005/058,851 discloses a composite tube for an ethylene pyrolysisfurnace and methods of manufacture and joining same wherein the tubecomprises an outer shell made from a wrought or cast heat resistantalloy and an inner core made from another alloy whose compositionapproximates a powder form. Both outer shell and inner core may beextruded to form the process tubes.

U.S. Pat. No. 5,873,951, assigned to Alon, Inc., issued on Feb. 23, 1999shows a diffusion coated ethylene furnace process tube in which theinner surface of the process tubes are diffusion coated with asufficient amount of chromium or chromium and silicon to form a firstcoating having a thickness of at least two mils which is then cleaned,neutralized and grit blasted. A second coating of aluminum or aluminumand silicon is then diffused onto the first coating to form a totalcoating thickness of at least five mils; the second coating is alsocleaned and polished to provide a smooth uniform surface. Reportedly,less coking occurs in these coated tubes.

U.S. Pat. No. 6,139,649, also assigned to Alon, Inc., issued on Oct. 31,2000, teaches a diffusion method for coating high temperature nickelchromium alloy products which produces ethylene furnace process tubeshaving a high temperature nickel chromium alloy product coated on theinner surface thereof. The inner coating has a first layer of chromiumor chromium and silicon covered by a second layer of aluminum,magnesium, silicon and manganese which in turn is covered by a thirdlayer of rare earth metals such as yttrium and zirconium. After eachlayer is applied the tube is heat treated, and finally after the finallayer has been applied the final surface is treated with argon andnitrogen to stabilize the surface oxides, and can be polished tominimize sites for carbon buildup. Less coking occurs in these coatedprocess tubes.

U.S. Pat. No. 6,537,388 issued on Mar. 25, 2003 and also assigned toAlon, Inc. discloses a surface alloy system conversion for hightemperature applications in which chromium, silicon, aluminum, andoptionally manganese are diffused onto the surface of a high temperatureally product, to provide a coating having improved resistance tocarburization and catalytic coke formation.

U.S. Pat. No. 6,337,459 issued on Jan. 8, 2002 and assigned to DaidoTokushuko Kabushiki Kaisha teaches a multi-layered anti-coking heatresisting metal tube and a method of manufacturing the process tube inwhich a preferably powdered alloy is applied to the inner and/or outersurface of the process tube.

PCT application International Publication No. WO2007/064288 published onJun. 7, 2007, and applied for by Sandvik Intellectual Property ABdiscloses a metallic tube for heating a medium or subject outside orinside thereof by heat transfer thorough the walls of the tube in whicha layer of essential Al₂O₃ is formed on the surfaces thereof when heatedto at least 750° C. At least one of the external and the internalsurface of the tube is coated by one of a metal, metal alloy and metalcompound, which after oxidation forms as a layer having an emissivitycoefficient exceeding 0.7 or by a layer essentially consisting of ametal oxide which has an emissivity coefficient exceeding 0.7.

Although, the majority of reaction cracking lines are comprised ofmetallic tubes, alternative compositions of the reaction cracking linesare possible. For example, U.S. Pat. No. 6,312,652 issued on Nov. 6,2001 and assigned to Stone & Webster Engineering Corp. discloses aceramic drip pipe and tube reactor for ethylene production. The reactionlines of the furnace are fabricated of a ceramic refractory feed inletpipe coaxially located with a ceramic refractory tube to define anannular space therebetween which is, in part, located without and withinthe radiant heating firebox volume of such furnace, this to provide fora zone wherein hot cracked olefin product gas is quenched in temperaturein such annular space outside of the firebox and a cracking zone withinthe firebox within which hydrocarbon feed is cracked to an olefincontaining product gas composition. The ceramic refractory materialconstruction of the '652 patent permits such a pipe-tube reaction linestructure to be exposed to a much greater heat/temperature content ofwhich the firebox is capable than reaction lines of conventionalmetallic construction. Cracking predominantly occurs within the annularspace, meaning that the cylindrical ceramic refractory structures may beof diameters sufficient to provide for high strength structures. Greaterfirebox temperatures allow the use of a shorter reaction line structure.

U.S. Pat. No. 6,497,809 issued on Dec. 24, 2002 and assigned to PhillipsPetroleum Company discloses a method for prolonging the effectiveness ofa pyrolytic cracking tube treated for the inhibition of coke formationduring cracking in which the tubes have tin and silicon deposited on thesurface exposed to the hydrocarbon feed functioning as an antifoulantfor inhibiting the formation of coke to desulfurize a sulfur-containingfeedstock.

SUMMARY OF THE INVENTION

The present invention, drawn to pyrolysis furnace constructions andprocess used in the production of vinyl chloride monomers, each furnaceconstruction includes a firebox defining a chamber having a thermalprotective layer disposed on at least part of the refractory wallsand/or on at least one process tube disposed within the firebox chamber.The thermal protective layer consisting of a high emissivitymultifunctional coating. The thermal protective layer is disposed on theexposed surfaces within the firebox, including the external surfaces ofthe process tubes, and within the process tubes. The refractory wallsare covered with refractory material, including bricks, castables orthermal ceramic fiber, as is well known in the art, and are composed ofsilica, fireclay, high alumina, and the like and combinations thereof,as is also known in the art.

Vaporized EDC is dried and passed over a catalyst packed in the processtubes that are directly heated in a cracking furnace. The hot effluentgases are quenched and the condensed gases fed into a fractionatingtower operating under pressure. The product VCM is formed by condensingthe overhead vapors in a water condenser. The VCM is then filtered andsent to either a storage tank for further processing to produce PVC orsold to other manufacturers that make PVC.

The thermal protective layer on the metal/alloy surfaces of processtubes may contain from about 5% to about 30% of an inorganic adhesive,from about 45% to about 92% of a filler, and from about 2% to about 20%of one or more emissivity agents, in a dry admixture. An alternativethermal protective layer which may be disposed on ceramic surfaces ofeither refractory wall or process tubes may contain from about 5% toabout 35% of colloidal silica, from about 23% to about 79% of a filler,and from about 2% to about 20% of one or more emissivity agents. Eitherthermal protective layer of the present invention may further containfrom about 1% to about 5% of a stabilizer.

An aspect of the present invention is that the thermal protective layerlimits coking; therefore, less maintenance is required, resulting inless downtime, and increasing the amount of continuous production runspossible.

Another aspect of the present invention is that it generates uniformheating of the refractory walls and process tubes, Uniform heating ofthe refractory walls results in improved cracking ratios, lessmaintenance, energy savings and increased production.

Yet another aspect of the present invention is a dramatic increase incost efficiently and production. Overall, the cost efficiency andproduction yields are increased permitting a greater profit and lesswaste.

A further aspect of the present invention is that it reduces the outsideskin temperature of the furnace.

Yet a further aspect of the present invention is the increased heattransfer from the furnace refractory walls to the process tubes and theincreased thermal flux across the tubes, and improves the crackingrate/ratio.

These and other aspects of the present invention will become readilyapparent upon further review of the following drawings andspecification.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the described embodiments are specifically setforth in the appended claims; however, embodiments relating to thestructure and process of making the present invention, may best beunderstood with reference to the following description and accompanyingdrawings.

FIG. 1 is a block diagram demonstrating alternative processes to makevinyl chloride monomer according to the present invention.

FIG. 2 is a schematic illustration of an embodiment of a crackingfurnace having a thermal protective layer according to the presentinvention disposed on heat exposed surfaces thereof.

FIGS. 3 a and 3 b are side views of coated refractory brick according toan embodiment of the present invention.

FIGS. 4 a through 4 c are cross sectional views of thermal protectivelayered process tubes according to alternative embodiments of thepresent invention.

FIGS. 5 a and 5 b are schematic illustrations of an additionalembodiment of a cracking furnace, utilizing a tube within a tubeconfiguration, having a thermal protective layer according to thepresent invention disposed upon heat exposed surfaces thereof.

FIGS. 6 a through 6 c are sectional side views of emissivity coatedprocess tubes according to the alternative embodiment of FIGS. 5 a and 5b of the present invention.

Similar reference characters denote corresponding features consistentlythroughout the attached drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The block diagram 112 of FIG. 1 details the process and apparatus forproducing VCM from EDC. In the direct chlorination process 136, ethylene114 and chlorine 116 are reacted together at 136 to form EDC 120.Alternatively or additionally, in the oxygen chlorination process 134,oxygen 118 is reacted with HCl 132, with steam, to form EDC 120.Vaporized EDC 120 is dried and typically passed over a catalyst packedin stainless steel tubes 14, shown in FIGS. 2 and 4A through 6C that aredirectly heated in a cracking furnace 124. The hot effluent gases arequenched in a quencher 126 and the condensed gases fed into afractionating tower 128 operating under pressure to separate the productVCM 130 from HCl 132 and excess EDC, not shown in FIG. 1 but the excessEDC may be recycled in the same fashion as the HCl 132. The product VCM130 is formed by condensing the vapors in a water condenser. The VCM 130is then filtered and sent to either a storage tank for furtherprocessing to produce PVC or sold to other manufacturers that make PVC.

The overall reactions involved in the process of FIG. 1 are directchlorination where C₂H₄+Cl₂→C₂H₄Cl₂, and oxygen chlorination whereC₂H₄+2HCl+½H₂O→C₂H₄Cl₂+H₂O. The reaction for the EDC cracking isC₂H₄Cl₂→C₂H₂Cl+HCl, where the excess HCl may optionally be recycled backinto the oxygen chlorination reaction. The excess EDC may be recycled ineither direct or oxygen chlorination processes.

A cracking furnace 124 construction, as shown in FIG. 2, includes afirebox 12 defining a chamber 20 having walls 17, and containing aplurality of heat H generating burners 22 disposed within the fireboxchamber 20, each wall 17 having an internal refractory surface 19exposed to heat H generated by the burners 22. A tube structure 25having at least one process tube 14 disposed within the firebox chamber20, and in fluid communication therethrough, permitting fluid to passthrough the firebox chamber 20 while the fluid therein is containedentirely within the tube structure 25. The term “fluid” as used hereinincludes both liquid and gas. Excess heat H is allowed to vent throughan exhaust E. Each process tube 14 has an internal surface 21 definingan interior space, and an external surface 23 directly exposed to theheat H generated within the firebox chamber 20 for thermal communicationthrough the process tube 14 to heat the fluid mixture therein. Eachprocess tube 14, in this embodiment, extends from a first end 26 to asecond end 24 allowing fluid communication therethrough. The EDCfeedstock comprising is feed into the process tube structure 25 at theinlet R and the cracked product mixture is feed out to the quencher at Pto form the VCM.

As shown in FIGS. 4 a through 4 c, a thermal protective layer 18consisting of a high emissivity multifunctional nano coating disposed onthe external surface 23 of the process tube 14, on the internal surface21 of the process tube 14, or on combinations thereof. A thermalprotective layer 18 may be disposed on at least a part of the internalsurface 19 of the firebox chamber 20. In some firebox chambers 20, atleast part of at least a refractory wall 17 is composed of a pluralityof refractory bricks 16 disposed therein forming the internal surface 19of the firebox chamber 20. In other firebox chambers, castable orceramic fiber is used to form the refractory surface of the fireboxchamber 20, as is well known in the art. The thermal protective layer 18may be disposed upon the refractory bricks 16, as shown in FIGS. 3 a and3 b, or on the surface of castable or ceramic fiber refractory walls.

Examples of refractory walls include Empire (trademark) S, which is ahigh duty dry press fireclay brick, Clipper (trademark), Korundal XD(trademark) and Insblok-19 available from A.P. Green Industries, Inc.(of Mexico, Mo.). An example of a ceramic fiber refractory includesInsboard 2300 LD also available form A.P. Green Industries, Inc. Theserefractory materials contains approximately 9.7% to 61.5% silica (SiO₂),12.1% to 90.0% alumina (Al₂O₃), 0.2% to 1.7% iron oxide (Fe₂O₃), up to27.7% lime (CaO), 0.1% to 0.4% magnesia (MgO), 2.0% to 6.3% titania(TiO₂) and 0.1% to 2.4% of alkalies (Na₂O plus K₂O).

In an alternative cracking furnace construction 124, as shown in FIGS. 5a and 5 b, a second process tube 28 is provided about the first processtube 14 and encompassing the first process tube 14 therein, as shown.The second process tube 28 have first and second ends 29 and 31, whereinthe second end 31 is closed, as shown. A fluid entering through thefirst end 27 of the first thermal tube 14 is ejected out of an opening25 dispose adjacent the first end 29 of the second thermal tube 28.

A conventional means for feeding the EDC containing feed stock fluidmixture R into the tube structure 25 adjacent the first end 24 whereinthe feed stock fluid mixture flows through the interior space of eachrefractory tube 14 from first 24 through second ends 26, and is heatedtherein by thermal communication through the process tube 14,discharging a cracked hydrocarbon product containing VCM fluid mixture Pout of the tube structure 25. A quencher 126 for receiving the crackedhydrocarbon product containing VCM fluid mixture when it is dischargedfrom the tube structure 25 also is provided. Various tube 14configurations exist but each define interior spaces and have internaland external surfaces thereof.

The thermal protective layer 18 may be applied as a high emissivitymultifunctional thermal protective coating. Suitable coatings andmethods of application are described in U.S. Pat. Nos. 7,105,047 and6,921,431 and assigned to Wessex Incorporated, the contents of which areincorporated herein in their entirety.

A high emissivity coating suitable for forming a thermal protectivelayer on a metal/alloy process tube assembly of the present inventionmay contain from about 5% to about 30% of an inorganic adhesive, fromabout 45% to about 92% of a filler, and from about 1% to about 20% ofone or more emissivity agents, in a dry admixture. Preferably, the dryadmixture also contains from about 1% to about 5% of a stabilizer.

An alternative high emissivity coating suitable for forming a thermalprotective layer on a ceramic process tubes and assembly, and on ceramicrefractory wall materials, including brick, castable and ceramic fiberrefractory walls, according to an embodiment of the present inventionmay contain from about 5% to about 35% of colloidal silica, from about23% to about 79% of a filler, from about 1% to about 20% of one or moreemissivity agents. Preferably, a thermal protective layer of the presentinvention also contains from about 1.5% to about 5.0% of a stabilizer.

As used herein, all percentages (%) are percent weight-to-weight, alsoexpressed as weight/weight %, % (w/w), w/w, w/w % or simply %, unlessotherwise indicated. Also, as used herein, the terms “wet admixture”refers to relative percentages of the composition of the thermalprotective coating in solution and “dry admixture” refers to therelative percentages of the composition of the dry thermal protectivecoating mixture prior to the addition of water. In other words, the dryadmixture percentages are those present without taking water intoaccount. Wet admixture refers to the admixture in solution (with water).“Wet weight percentage” is the weight in a wet admixture, and “dryweight percentage” is the weight in a dry admixture without regard tothe wet weight percentages. The term “total solids”, as used herein,refers to the total sum of the silica/alumina and the alkali or ammonia(NH₃), plus the fraction of all solids including impurities. Weight ofthe solid component divided by the total mass of the entire solution,times one hundred, yields the percentage of “total solids”.

Method of preparation of coating involves applying a wet admixture ofthe coating to the surface to be coated. Alternative methods may includespraying the wet admixture on the surface or atomizing the dry admixtureand coating the surface accordingly.

In a coating solution according to the present invention, a wetadmixture of the thermal protective coating, to be applied tometal/alloy process tubes/assembly, contains from about 6% to about 40%of an inorganic adhesive, from about 23% to about 46% of a filler, fromabout 0.5% to about 10% of one or more emissivity agents, and from about18% to about 50% water. In order to extend the shelf life of the coatingsolution, from about 0.5% to about 2.5% of a stabilizer is preferablyadded to the wet admixture. The wet admixture coating solution containsbetween about 40% and about 60% total solids.

In a coating solution according to the present invention, a wetadmixture of an alternative thermal protective coating, to be applied tothe refractory structure and ceramic process tubes/assembly, containsfrom about 15% to about 45% of colloidal silica, from about 23% to about55% of a filler, from about 0.5% to about 10% of one or more emissivityagents, from about 0.5% to about 2.5% of a stabilizer and from about 18%to about 40% water. The wet admixture coating solution contains betweenabout 40% and about 70% total solids.

The inorganic adhesive is preferably an alkali/alkaline earth metalsilicate taken from the group consisting of sodium silicate, potassiumsilicate, calcium silicate, and magnesium silicate. The colloidal silicais preferably a mono-dispersed distribution of colloidal silica, andtherefore, has a very narrow range of particle sizes. The filler ispreferably a metal oxide taken from the group consisting of silicondioxide, aluminum oxide, titanium dioxide, magnesium oxide, calciumoxide and boron oxide. The emissivity agent(s) is preferably taken fromthe group consisting of silicon hexaboride, carbon tetraboride, silicontetraboride, silicon carbide, molybdenum disilicide, tungstendisilicide, zirconium diboride, cupric chromite, and metallic oxidessuch as iron oxides, magnesium oxides, manganese oxides, copper chromiumoxides, and chromium oxides, cerium oxides, and terbium oxides, andderivatives thereof. The copper chromium oxide, as used in the presentinvention, is a mixture of cupric chromite and cupric oxide. Thestabilizer may be taken from the group consisting of bentonite, kaolin,magnesium alumina silica clay, tabular alumina and stabilized zirconiumoxide. The stabilizer is preferably bentonite. Other ball claystabilizers may be substituted herein as a stabilizer. Colloidalalumina, in addition to or instead of colloidal silica, may also beincluded in the admixture of the present invention. When colloidalalumina and colloidal silica are mixed together one or the otherrequires surface modification to facilitate mixing, as is known in theart.

Coloring may be added to the protective coating layer of the presentinvention to depart coloring to the tubes. Inorganic pigments may beadded to the protective coating without generating toxic fumes. Ingeneral, inorganic pigments are divided into the subclasses: colored(salts and oxides), blacks, white and metallic. Suitable inorganicpigments include but are not limited to yellow cadmium, orange cadmium,red cadmium, deep orange cadmium, orange cadmium lithopone and redcadmium lithopone.

A preferred embodiment of the present invention contains a dry admixtureof from about 10% to about 25% sodium silicate, from about 50% to about79% silicon dioxide powder, and from about 4% to about 15% of one ormore emittance agent(s) taken from the group consisting of iron oxide,boron silicide, boron carbide, silicon tetraboride, silicon carbidemolybdenum disilicide, tungsten disilicide, zirconium diboride.Preferred embodiments of the thernal coating may contain from about 1.0%to about 5.0% bentonite powder in dry admixture. The correspondingcoating in solution (wet admixture) for this embodiment contains fromabout 10.0% to about 35.0% sodium silicate, from about 25.0% to about50.0% silicon dioxide, from about 18.0% to about 39.0% water, and fromabout 1.0% to about 8.5% one or more emittance agent(s). This wetadmixture must be used immediately. In order to provide a coatingsolution admixture (wet admixture), which may be stored and used later,preferred embodiments of the thermal coating contain from about 0.25% toabout 2.50% bentonite powder. Preferably deionized water is used.Preferred embodiments of the wet admixture have a total solids contentranging from about 45% to about 55%.

A preferred thermal protective coating of the present invention containsa dry admixture from about 15.0% to about 20.0% sodium silicate, fromabout 69.0% to about 79.0% silicon dioxide powder, about 1.00% bentonitepowder, and from about 5.00% to about 15.0% of an emittance agent. Theemittance agent is taken from one or more of the following: iron oxide,boron silicide, and boron carbide.

A most preferred wet admixture contains about 20.0% sodium silicatebased on a sodium silicate solids content of about 37.45%, from about34.5% to about 39.5% silicon dioxide powder, about 0.500% bentonitepowder, and from about 2.50% to about 7.5% of an emittance agent, withthe balance being water. The emittance agent is most preferably takenfrom the group consisting of iron oxide, boron silicide, and boroncarbide (also known as, carbon tetraboride). Preferred embodimentsinclude those where the emittance agent comprises about 2.50% ironoxide, about 2.50% to about 7.5% boron silicide, or from about 2.50% toabout 7.50% boron carbide. The pH of a most preferred wet admixtureaccording to the present invention is about 11.2.±.1.0, the specificgravity is about 1.45.±.0.05 and the total solids content is about50.±.0.3%.

A preferred embodiment of the present invention contains a dry admixtureof from about 10.0% to about 30.0% colloidal silica, from about 50% toabout 79% silicon dioxide powder, and from about 2% to about 15% of oneor more emittance agent(s) taken from the group consisting of ceriumoxide, boron silicide, boron carbide, silicon tetraboride, siliconcarbide molybdenum disilicide, tungsten disilicide, zirconium diboride,and from about 1.5% to about 5.0% bentonite powder. The correspondingcoating in solution (wet admixture) for this embodiment contains fromabout 20.0% to about 35.0% colloidal silica, from about 25.0% to about55.0% silicon dioxide, from about 18.0% to about 35.0% water, and fromabout 2.0% to about 7.5% one or more emittance agent(s), and from about0.50% to about 2.50% bentonite powder. Preferably deionized water isused. Preferred embodiments of the wet admixture have a total solidscontent ranging from about 50% to about 65%.

A most preferred thermal protective coating of the present inventioncontains a dry admixture from about 15.0% to about 25.0% colloidalsilica, from about 68.0% to about 78.0% silicon dioxide powder, about2.00% to about 4.00% bentonite powder, and from about 4.00% to about6.00% of an emittance agent. The emittance agent is taken from one ormore of the following: zirconium boride, boron silicide, and boroncarbide.

A most preferred wet admixture contains about 27.0% colloidal silicabased on a colloidal silica solids content of about 40%, from about 25%to about 50% silicon dioxide powder, about 1.50% bentonite powder, andfrom about 2.50% to about 5.50% of an emittance agent, with the balancebeing water. The emittance agent is most preferably taken from the groupconsisting of zirconium boride, boron silicide, and boron carbide.Preferred embodiments include those where the emittance agent comprisesabout 2.50% zirconium diboride, about 2.50% boron silicide, or fromabout 2.50% to about 7.50% boron carbide. The specific gravity of a mostpreferred wet admixture is about 1.40 to 1.50 and the total solidscontent is about 50% to 60%.

An inorganic adhesive, which may be used in the present invention,includes N (trademark) type sodium silicate that is available from thePQ Corporation (of Valley Forge, Pa.). Sodium silicates (Na₂O.XSiO₂) aremetal oxides of silica. All soluble silicates can be differentiated bytheir ratio, defined as the weight proportion of silica to alkali(SiO₂/Na₂O). Ratio determines the physical and chemical properties ofthe coating. The glassy nature of silicates imparts strong and rigidphysical properties to dried films or coatings. Silicates air dry to aspecific moisture level, according to ambient temperature and relativehumidity. Heating is necessary to take these films to complete dryness—acondition in which silicates become nearly insoluble. Reaction withother materials, such as aluminum or calcium compounds, will make thefilm coating completely insoluble. The N (trademark) type sodiumsilicate, as used in the examples below, has a weight ratioSiO.sub.2/Na.sub.2O is 3.22, 8.9% Na.sub.2O, 28.7% SiO.sub.2, with adensity (at room temperature of 20° C.) of 41.0°Be′, 11.6 lb/gal or 1.38g/cm.sup.3. The pH is 11.3 with a viscosity of 180 centipoises. The Ntype sodium silicate is in a state of a syrupy liquid.

The term “total solids” refers to the sum of the silica and the alkali.The weight ratio is a most important silicate variable. Ratio determinesthe product solubility, reactivity and physical properties. Ratio iseither the weight or molar proportion of silica to alkali. Density is anexpression of total solids and is typically determined using ahydrometer or pycnometer

Ludox (trademark) TM 50 colloidal silica and Ludox (trademark) AS 40colloidal silica are available from Grace Davidson (of Columbia, Md.).The particles in Ludox (trademark) colloidal silica are discrete uniformspheres of silica which have no internal surface area or detectablecrystallinity. Most are dispersed in an alkaline medium which reactswith the silica surface to produce a negative charge. Because of thenegative charge, the particles repel one another resulting in stableproducts. Although most grades are stable between pH 8.5-11.0, somegrades are stable in the neutral pH range. Ludox (trademark) colloidalsilicas are aqueous colloidal dispersions of very small silicaparticles. They are opalescent to milky white liquids. Because of theircolloidal nature, particles of Ludox (trademark) colloidal silica have alarge specific surface area which accounts for the novel properties andwide variety of uses. Ludox (trademark) colloidal silica is available intwo primary families: mono-dispersed, very narrow particle sizedistribution of Ludox (trademark) colloidal silica and poly-dispersed,broad particle size distribution of Ludox (trademark) P. The Ludox(trademark) colloidal silica is converted to a dry solid, usually bygelation. The colloidal silica can be gelled by (1) removing water, (2)changing pH, or (3) adding a salt or water-miscible organic solvent.During drying, the hydroxyl groups on the surface of the particlescondense by splitting out water to form siloxane bonds (Si—O—Si)resulting in coalescence and interbonding. Dried particles of Ludox(trademark) colloidal silica are chemically inert and heat resistant.The particles develop strong adhesive and cohesive bonds and areeffective binders for all types of granular and fibrous materials,especially when use at elevated temperature is required.

Colloidal alumina is available as Nyacol (trademark) colloidal alumina,and specifically, Nyacol (trademark) AL20, available from Nyacol NanoTechnologies, Inc. (Ashland, Mass.), and is available in deionized waterto reduce the sodium and chlorine levels to less than 10 ppm. Itcontains about 20 percent by weight of AL₂O₃, a particle size of 50 nm,positive particle charge, pH 4.0, specific gravity of 1.19, and aviscosity of 10 cPs.

The filler may be a silicon dioxide powder such as Min-U-Sil (trademark)5 silicon dioxide available from U.S. Silica (of Berkeley Springs, W.Va.). This silicon dioxide is fine ground silica. Chemical analysis ofthe Min-U-Sil (trademark) silicon dioxide indicates contents of 98.5%silicon dioxide, 0.060% iron oxide, 1.1% aluminum oxide, 0.02% titaniumdioxide, 0.04% calcium oxide, 0.03% magnesium oxide, 0.03% sodiumdioxide, 0.03% potassium oxide and a 0.4% loss on ignition. The typicalphysical properties are a compacted bulk density of 41 lbs/ft.sup.3, anuncompacted bulk density of 36 lbs/ft³, a hardness of 7 Mohs, hegman of7.5, median diameter of 1.7 microns, an oil absorption (D-1483) of 44, apH of 6.2, 97%−5 microns, 0.005%+325 Mesh, a reflectance of 92%, a 4.2yellowness index and a specific gravity of 2.65.

Emittance agents are available from several sources. Emissivity is therelative power of a surface to absorb and emit radiation, and the ratioof the radiant energy emitted by a surface to the radiant energy emittedby a blackbody at the same temperature. Emittance is the energyreradiated by the surface of a body per unit area.

The boron carbide, also known as carbon tetraboride, which may be usedas an emissivity agent in the present invention, is sold as 1000 W boroncarbide and is available from Electro Abrasives (of Buffalo, N.Y.).Boron Carbide is one of the hardest man made materials available. Above1300° C., it is even harder than diamond and cubic boron nitride. It hasa four point flexural strength of 50,000 to 70,000 psi and a compressivestrength of 414,000 psi, depending on density. Boron Carbide also has alow thermal conductivity (29 to 67 W/mK) and has electrical resistivityranging from 0.1 to 10 ohm-cm. Typical chemical analysis indicates 77.5%boron, 21.5% carbon, iron 0.2% and total Boron plus Carbon is 98%. Thehardness is 2800 Knoop and 9.6 Mohs, the melting point is 4262° F.(2350° C.), the oxidation temperature is 932° F. (500° C.), and thespecific gravity is 2.52 g/cc.

1000 W green silicon carbide (SiC), an optional emissivity agent, isalso available from Electro Abrasives. Green Silicon Carbide is anextremely hard (Knoop 2600 or Mohs 9.4) man made mineral that possesseshigh thermal conductivity (100 W/m-K). It also has high strength atelevated temperatures (at 1100° C., Green SiC is 7.5 times stronger thanAl₂O₃). Green SiC has a Modulus of Elasticity of 410 GPa, with nodecrease in strength up to 1600° C., and it does not melt at normalpressures but instead dissociates at 2815.5° C. Green silicon carbide isa batch composition made from silica sand and coke, and is extremelypure. The physical properties are as follows for green silicon carbide:the hardness is 2600 Knoop and 9.4 Mohs, the melting point is 4712° F.(2600° C.), and the specific gravity is 3.2 g/cc. The typical chemicalanalysis is 99.5% SiC, 0.2% SiO₂, 0.03% total Si, 0.04% total Fe, and0.1% total C. Commercial silicon carbide and molybdenum disilicide mayneed to be cleaned, as is well known in the art, to eliminate flammablegas generated during production.

Boron silicide (B₆Si) (Item # B-1089) is available from Cerac (ofMilwaukee, Wis.). The boron silicide, also known as silicon hexaboride,available from Cerac has a −200 mesh (about 2 microns average) and atypical purity of about 98%. Zirconium boride (ZrB₂) is also availablefrom Cerac with a typical average of 10 microns or less (−325 mesh), anda typical purity of about 99.5%.

Iron oxide available from Hoover Color (of Hiwassee, Va.) is a syntheticblack iron oxide (Fe₂O₃) which has an iron oxide content of 60%, aspecific gravity of 4.8 gm/cc, a tap density (also known as, bulkdensity) of 1.3 gm/cc, oil absorption of 15 lbs/100 lbs, a 325 meshresidue of 0.005, and a pH ranging from 7 to 10.

Preferably the admixture of the present invention includes bentonitepowder, tabular alumina, or magnesium alumina silica clay. The bentonitepowder permits the present invention to be prepared and used at a laterdate. Preparations of the present invention without bentonite powdermust be used immediately. The examples provided for the presentinvention include PolarGel bentonite powder are available from Mineraland Pigment Solutions, Inc. (of South Plainfield, N.J.). Technical gradebentonite is generally used for the purpose of suspending, emulsifyingand binding agents, and as Theological modifiers. The typical chemicalanalysis 59.00% to 61.00% of silicon dioxide (SiO₂), 20.00% to 22.00% ofaluminum oxide (Al₂O₃), 2.00% to 3.00% calcium oxide (CaO), 3.50% to4.30% magnesium oxide (MgO), 0.60% to 0.70% ferric oxide (Fe₂O₃), 3.50%to 4.00% sodium oxide (Na₂O), 0.02% to 0.03% potassium oxide (K₂O), and0.10% to 0.20% titanium dioxide and a maximum of 8.0% moisture. The pHvalue ranges from 9.5 to 10.5. Typical physical properties are 83.0 to87.0 dry brightness, 2.50 to 2.60 specific gravity, 20.82 pounds/solidgallon, 0.0480 gallons for one pound bulk, 24 ml minimum swelling power,maximum 2 ml gel formation, and 100.00% thru 200 mesh. Tabular alumina(Alumina Tab T64 Item 635) and magnesium alumina silica clay (Mag AlumSil Technical Item 105) are also available from Mineral and PigmentSolutions, Inc.

The admixture of the present invention preferably includes bentonitepowder, tabular alumina, or other magnesium alumina silica clay as thestabilizer. The bentonite powder permits the present invention to beprepared and used at a later date. The examples provided for the presentinvention include PolarGel bentonite powder (Item #354) available fromMineral and Pigment Solutions, Inc. (of South Plainfield, N.J.).Bentonite is generally used for the purpose of suspending, emulsifyingand binding agents, and as rheological modifiers. The typical chemicalanalysis is 59.00% to 61.00% of silicon dioxide (SiO₂), 20.00% to 22.00%of aluminum oxide (Al₂O₃), 2.00% to 3.00% calcium oxide (CaO), 3.50% to4.30% magnesium oxide (MgO), 0.60% to 0.70% ferric oxide (Fe₂O₃), 3.50%to 4.00% sodium oxide (Na₂O), 0.02% to 0.03% potassium oxide (K₂O), and0.10% to 0.20% titanium dioxide and a maximum of 8.0% moisture. The pHvalue ranges from 9.5 to 10.5. Typical physical properties are 83.0 to87.0 dry brightness, 2.50 to 2.60 specific gravity, 20.82 pounds/solidgallon, 0.0480 gallons for one pound bulk, 24 ml minimum swelling power,maximum 2 ml gel formation, and 100.00% thru 200 mesh. Tabular alumina(Alumina Tab T64 Item 635) and magnesium alumina silica clay (Mag AlumSil Technical Item 105) are also available from Mineral and PigmentSolutions, Inc.

Colorants, which may be added to the present invention, include but arenot limited to inorganic pigments. Suitable inorganic pigments, such asyellow iron oxide, chromium oxide green, red iron oxide, black ironoxide, titanium dioxide, are available from Hoover Color Corporation.Additional suitable inorganic pigments, such as copper chromite blackspinel, chromium green-black hematite, nickel antimony titanium yellowrutile, manganese antimony titanium buff rutile, and cobalt chromiteblue-green spinel, are available from The Shepherd Color Company (ofCincinnati, Ohio).

A surfactant may be added to the wet admixture prior to applying thethermal protective layer to the support layer. The surfactant wassurfyonol (trademark) 465 surfactant available from Air Products andChemicals, Inc. (of Allentown, Pa.). The surfyonol (trademark) has achemical structure of ethoxylated 2,4,7,9-tetramethyl 5 decyn-4,7-diol.Other surfactants may be used, such as STANDAPOL (trademark) T, INCIwhich has a chemical structure of triethanolamine lauryl sulfate, liquidmild primary surfactant available from Cognis-Care Chemicals (ofCincinnati, Ohio). The amount of surfactant present by weight in the wetadmixture in from about 0.05% to about 0.2%.

The thermal protective coating is applied to the surface to form athermal protective layer. The substrate surface may be a metallicsubstrate such as iron, aluminum, alloys, steel, cast iron, stainlesssteel and the like, or it may be a ceramic surface, as is well known inthe art. The coating is typically applied wet, and either allowed to airdry or heat dry.

Surface preparation for metal or ceramic structures are similar. Thesurface should be clear of all dirt, loose material, surfactants, oils,gasses, etc. A metal surface may be grit blasted. Grit blasting isdesirable to remove oxidation and other contaminants for metal surfacesonly. Grits media should be sharp particles. Gun pressure will varydepending on the cut type, condition of the metal and profile desired.Very old metal will require 70-80 psi. Oil and water-free compressed airis required. Proper filters for the removal of oil and water arerequired. Other alkaline type metal cleanses may also be utilized.

After the grit blast, the surface should be thoroughly cleaned to removeall loose particles with clean oil and water free air blasts. Avoidcontaminating surface with fingerprints. Acetone can be used (underproper ventilation and exercising all necessary precautions when workingwith acetone) on a clean cloth to wipe the surface clean. A cleaningcompound may be used on certain stainless steel in lieu of gritblasting. Durlum available from Blue Wave Ultrasonics (of Davenport,Iowa), a powdered alkaline cleaner, may be used in cleaning metalsurface,

When using the wet admixture containing a stabilizer, solids may settleduring shipment or storage. Prior to use all previously mixed coatingmust be thoroughly re-mixed to ensure all settled solids and clumps arecompletely re-dispersed. When not using a stabilizer, the coating maynot be stored for any period of time. In any case, the coating should beused immediately after mixing to minimize settling.

Mixing instructions for one and five gallon containers. High speed/highshear saw tooth dispersion blade 5″ diameter for one gallon containersand 7″ diameter for five gallon containers may be attached to a handdrill of sufficient power with a minimum no load speed of 2000 rpmshear. Dispersion blades can be purchased from numerous suppliers Mix athigh speed to ensure complete re-dispersion for a minimum of 30 minutes.

The product should be applied directly after cleaning a metal surface sominimal surface oxidation occurs. The product should be applied in aproperly ventilated and well lit area, or protective equipment should beused appropriate to the environment, for example within a firebox. Themixed product should not be filtered or diluted.

A high volume low pressure (HVLP) spray gun should be used with 20-40psi of clean, oil and water free air. Proper filters for removal of oiland water are required. Alternatively, an airless spray gun may be used.Other types of spray equipment may be suitable. The applicator shouldpractice spraying on scrap metal prior to spraying the actual part toensure proper coverage density. An airless spray system is preferablefor applications on ceramic surfaces such as the refractory materials.Suitable airless spray systems are available from Graco (of Minneapolis,Minn.). Suitable HVLP spray systems, which are desirable for metal/alloyprocess tubes, are available from G.H. Reed Inc. (of Hanover, Pa.). Ahigh speed agitator may be desirable. Suitable spray gun tips may beselected to provide the proper thickness without undue experimentation.

Controlling the coverage density may be critical to coating performance.The thermal layer thickness should be from about two (2) mils (about 50microns (μ)) to about ten (10) mils (about 255μ), depending upon typed,size and condition of substrate. One (1) mil equals 25.4μ. Properthickness may vary. If possible, rotate the part 90 degrees at leastonce to maintain even coverage, Allow 1 to 4 hours of dry time beforethe part is handled, depending upon humidity and temperature.

An example of the present invention was carried out using a VCM furnacewith a production of 40,000 pounds per hour, natural gas fuel type, anannual usage of 450,000 MMBTU, with furnace controls that areprogrammable logic controls controlled by heat distribution in firebox.The VCM furnace had aged fire brick and metal incoloy tubes that werecoated with a thermal protective coating according to the presentinvention. The EDC is cracked at 1400° F. to 1450° F. The coated VCMfurnace performed with exceptional results within days of activation.Initial energy savings were instantaneously 7% with no furnaceadjustments, along with a production increase.

A VCM furnace containing aged fire brick with a thermal protective layerthereon. The thermal protective layer contained 15.0% sodium silicate,79.0% silicon dioxide powder, 5.0% boron carbide, and 1.0% bentonitepowder. The thermal protective layer was applied to aged fire brick as athermal protective coating containing 20.0% sodium silicate, 39.5%silicon dioxide powder, 2.5% boron carbide, 0.50% bentonite powder, and37.5% deionized water.

The metal incoloy tubes were coated with with a thermal protective layerthereon. The thermal protective layer contained 16.5% colloidal silica,76.3% silicon dioxide powder, 4.3% silicon hexaboride, and 2.9%bentonite powder. The thermal protective layer was applied to the tubesas a thermal protective coating containing 26.81% colloidal silica,49.60% silicon dioxide powder, 2.80% silicon hexaboride, 1.88% bentonitepowder, and 18.91% deionized water.

The resulting improvements noted included a greater than 10% productionincrease, energy savings greater than 5%, improved cracking reaction inthe process tubes, improved thermal response, steam savings forpreproduction product heating, reduced maintenance and downtime, furnaceskin temperature reduces more then 20% and reduced air emissions. Theestimated economic savings include a fuel savings of three percent witha production increase of then percent. The tube life expected to doublefrom five to ten years. The resultant expected reduction in downtime andproduct cracking improvement should add to the savings.

It is to be understood that the present invention is not limited to theembodiments described above, but encompasses any and all embodimentswithin the scope of the following claims.

1. A process of manufacturing vinyl chloride monomers, comprising:cracking an ethylene dichloride feedstock in a pyrolysis furnace byfeeding the feedstock through at least one heated process tube havingfirst and second ends with an internal surface defining an interiorspace having a thermal protective layer disposed thereon, the thermalprotective layer containing a. from about 5% to about 30% of aninorganic adhesive, from about 45% to about 92% of a filler, and fromabout 1% to about 20% of one or more emissivity agents, or b. from about5% to about 35% of colloidal silica, colloidal alumina, or combinationsthereof; from about 23% to about 79% of a filler, from about 1% to about20% of one or more emissivity agents.
 2. The process of claim 1,wherein: the pyrolysis furnace comprises a firebox chamber havingrefractory walls with exposed surfaces, and a plurality of heatgenerating burners; and the at least one process tubes are disposed in aprocess tube structure disposed within the firebox chamber, and in fluidcommunication therethrough, permitting feedstock to pass through thefirebox chamber while fluidly contained solely within the process tubestructure, and an external surface directly exposed to heat generatedwithin the firebox chamber for thermal communication therethroughwherein a thermal protective layer consisting of a high emissivitycoating is disposed on the external surface of the process tubes, on theexposed surfaces of the refractory walls, or combinations thereof,wherein the thermal protective layer contains a. from about 5% to about30% of an inorganic adhesive, from about 45% to about 92% of a filler,and from about 1% to about 20% of one or more emissivity agents, or b.from about 5% to about 35% of colloidal silica, colloidal alumina, orcombinations thereof; from about 23% to about 79% of a filler, fromabout 1% to about 20% of one or more emissivity agents.
 3. The processof claim 1, wherein: the thermal protective layer further comprises fromabout 1.0% to about 5.0% of a stabilizer; the thermal protective layerfurther comprises a surfactant; the thermal protective layer furthercomprises a colorant; the inorganic adhesive is taken from the groupconsisting of an alkali/alkaline earth metal silicate taken from thegroup consisting of sodium silicate, potassium silicate, calciumsilicate, and magnesium silicate; the filler is taken from the groupconsisting of silicon dioxide, aluminum oxide, titanium dioxide,magnesium oxide, calcium oxide, and boron oxide; the one or moreemissivity agents are taken from the group consisting of siliconhexaboride, boron carbide, silicon tetraboride, silicon carbide,molybdenum disilicide, tungsten disilicide, zirconium diboride, cupricchromite, and metallic oxides; or combinations thereof; the stabilizeris taken from the group consisting of bentonite, kaolin, magnesiumalumina silica clay, tabular alumina, and stabilized zirconium oxide;the thermal protective layer is from about two (2) mils (about 50microns (μ)) to about ten (10) mils (about 255μ) thick; or combinationsthereof.
 4. The process of claim 1, wherein: a thermal protective layercontains a. from about 5% to about 30% of an inorganic adhesive, theinorganic adhesive is taken from the group consisting of analkali/alkaline earth metal silicate taken from the group consisting ofsodium silicate, potassium silicate, calcium silicate, and magnesiumsilicate; from about 45% to about 92% of a filler, the filler taken fromthe group consisting of silicon dioxide, aluminum oxide, titaniumdioxide, magnesium oxide, calcium oxide, and boron oxide; and from about1% to about 20% of one or more emissivity agents taken from the groupconsisting of silicon hexaboride, boron carbide, silicon tetraboride,silicon carbide, molybdenum disilicide, tungsten disilicide, zirconiumdiboride, cupric chromite, and metallic oxides; b. from about 5% toabout 35% of colloidal silica, colloidal alumina, or combinationsthereof; from about 23% to about 79% of a filler taken from the groupconsisting of silicon dioxide, aluminum oxide, titanium dioxide,magnesium oxide, calcium oxide, and boron oxide; and from about 1% toabout 20% of one or more emissivity agents taken from the groupconsisting of silicon hexaboride, boron carbide, silicon tetraboride,silicon carbide, molybdenum disilicide, tungsten disilicide, zirconiumdiboride, cupric chromite, and metallic oxides; c. from about 5% toabout 30% of an inorganic adhesive, the inorganic adhesive is taken fromthe group consisting of an alkali/alkaline earth metal silicate takenfrom the group consisting of sodium silicate, potassium silicate,calcium silicate, and magnesium silicate; from about 45% to about 92% ofa filler, the filler taken from the group consisting of silicon dioxide,aluminum oxide, titanium dioxide, magnesium oxide, calcium oxide, andboron oxide; and from about 1% to about 20% of one or more emissivityagents taken from the group consisting of silicon hexaboride, boroncarbide, silicon tetraboride, silicon carbide, molybdenum disilicide,tungsten disilicide, zirconium diboride, cupric chromite, and metallicoxides; and from about 1% to about 5% of a stabilizer taken from thegroup consisting of bentonite, kaolin, magnesium alumina silica clay,tabular alumina, and stabilized zirconium oxide; or d. from about 5% toabout 35% of colloidal silica, colloidal alumina, or combinationsthereof; from about 23% to about 79% of a filler taken from the groupconsisting of silicon dioxide, aluminum oxide, titanium dioxide,magnesium oxide, calcium oxide, and boron oxide; and from about 1% toabout 20% of one or more emissivity agents taken from the groupconsisting of silicon hexaboride, boron carbide, silicon tetraboride,silicon carbide, molybdenum disilicide, tungsten disilicide, zirconiumdiboride, cupric chromite, and metallic oxides; and from about 1.5% toabout 5.0% of a stabilizer taken from the group consisting of bentonite,kaolin, magnesium alumina silica clay, tabular alumina, and stabilizedzirconium oxide.
 5. The process of claim 1, wherein: a thermalprotective layer contains a. from about 10% to about 30% sodiumsilicate, from about 50% to about 79% silicon dioxide powder, and fromabout 4% to about 15% of one or more emissivity agents taken fiom thegroup consisting of iron oxide, boron silicide, boron carbide, silicontetraboride, silicon carbide powder, molybdenum disilicide, tungstendisilicide, and zirconium diboride; b. from about 10% to about 30%sodium silicate, from about 50% to about 79% silicon dioxide powder,from about 4% to about 15% of one or more emissivity agents taken fromthe group consisting of iron oxide, boron silicide, boron carbide,silicon tetraboride, silicon carbide powder, molybdenum disilicide,tungsten disilicide, and zirconium diboride, and from about 1% to about5% of a stabilizer taken from the group consisting of bentonite, kaolin,magnesium alumina silica clay, tabular alumina, and stabilized zirconiumoxide; c. from about 10% to about 30% colloidal silica, from about 50%to about 79% silicon dioxide powder, and from about 2% to about 15% ofone or more emissivity agents taken from the group consisting of ironoxide, boron silicide, boron carbide, silicon tetraboride, siliconcarbide molybdenum disilicide, tungsten disilicide, and zirconiumdiboride; or d. from about 10% to about 30% colloidal silica, from about50% to about 79% silicon dioxide powder, from about 2% to about 15% ofone or more emissivity agents taken from the group consisting of ironoxide, boron silicide, boron carbide, silicon tetraboride, siliconcarbide molybdenum disilicide, tungsten disilicide, and zirconiumdiboride, and from about 1.5% to about 5.0% of a stabilizer taken fromthe group consisting of bentonite, kaolin, magnesium alumina silicaclay, tabular alumina, and stabilized zirconium oxide.
 6. The process ofclaim 1, wherein: a second thermal process tube is provided about thefirst thermal process tube encompassing the first thermal process tubetherein the thermal process tube having first and second ends, whereinthe second end is closed; such that a fluid entering through the firstend of the first thermal tube is ejected out of an opening disposeadjacent the first end of the second thermal tube.
 7. The process ofclaim 2, wherein: the thermal protective layer further comprises fromabout 1.0% to about 5.0% of a stabilizer; the thermal protective layerfurther comprises a surfactant; the thermal protective layer furthercomprises a colorant; the inorganic adhesive is taken from the groupconsisting of an alkali/alkaline earth metal silicate taken from thegroup consisting of sodium silicate, potassium silicate, calciumsilicate, and magnesium silicate; the filler is taken from the groupconsisting of silicon dioxide, aluminum oxide, titanium dioxide,magnesium oxide, calcium oxide, and boron oxide; the one or moreemissivity agents are taken from the group consisting of siliconhexaboride, boron carbide, silicon tetraboride, silicon carbide,molybdenum disilicide, tungsten disilicide, zirconium diboride, cupricchromite, and metallic oxides; or combinations thereof; the stabilizeris taken from the group consisting of bentonite, kaolin, magnesiumalumina silica clay, tabular alumina, and stabilized zirconium oxide;the thermal protective layer is from about two (2) mils (about 50microns (μ)) to about ten (10) mils (about 255μ) thick; or combinationsthereof.
 8. The process of claim 2, wherein: a thermal protective layercontains a. from about 5% to about 30% of an inorganic adhesive, theinorganic adhesive is taken from the group consisting of analkali/alkaline earth metal silicate taken from the group consisting ofsodium silicate, potassium silicate, calcium silicate, and magnesiumsilicate; from about 45% to about 92% of a filler, the filler taken fromthe group consisting of silicon dioxide, aluminum oxide, titaniumdioxide, magnesium oxide, calcium oxide, and boron oxide; and from about1% to about 20% of one or more emissivity agents taken from the groupconsisting of silicon hexaboride, boron carbide, silicon tetraboride,silicon carbide, molybdenum disilicide, tungsten disilicide, zirconiumdiboride, cupric chromite, and metallic oxides; b. from about 5% toabout 35% of colloidal silica, colloidal alumina, or combinationsthereof; from about 23% to about 79% of a filler taken from the groupconsisting of silicon dioxide, aluminum oxide, titanium dioxide,magnesium oxide, calcium oxide, and boron oxide; and from about 1% toabout 20% of one or more emissivity agents taken from the groupconsisting of silicon hexaboride, boron carbide, silicon tetraboride,silicon carbide, molybdenum disilicide, tungsten disilicide, zirconiumdiboride, cupric chromite, and metallic oxides; c. from about 5% toabout 30% of an inorganic adhesive, the inorganic adhesive is taken fromthe group consisting of an alkali/alkaline earth metal silicate takenfrom the group consisting of sodium silicate, potassium silicate,calcium silicate, and magnesium silicate; from about 45% to about 92% ofa filler, the filler taken from the group consisting of silicon dioxide,alunum oxide, titanium dioxide, magnesium oxide, calcium oxide, andboron oxide; and from about 1% to about 20% of one or more emissivityagents taken from the group consisting of silicon hexaboride, boroncarbide, silicon tetraboride, silicon carbide, molybdenum disilicide,tungsten disilicide, zirconium diboride, cupric chromite, and metallicoxides, and from about 1% to about 5% of a stabilizer taken from thegroup consisting of bentonite, kaolin, magnesium alumina silica clay,tabular alumina, and stabilized zirconium oxide; or d. from about 5% toabout 35% of colloidal silica, colloidal alumina, or combinationsthereof; from about 23% to about 79% of a filler taken from the groupconsisting of silicon dioxide, aluminum oxide, titanium dioxide,magnesium oxide, calcium oxide, and boron oxide; and from about 1% toabout 20% of one or more emissivity agents taken from the groupconsisting of silicon hexaboride, boron carbide, silicon tetraboride,silicon carbide, molybdenum disilicide, tungsten disilicide, zirconiumdiboride, cupric chromite, and metallic oxides; and from about 1.5% toabout 5.0% of a stabilizer taken from the group consisting of bentonite,kaolin, magnesium alumina silica clay, tabular alumina, and stabilizedzirconium oxide.
 9. The process of claim 2, wherein: a thermalprotective layer contains a. from about 10% to about 30% sodiumsilicate, from about 50% to about 79% silicon dioxide powder, and fromabout 4% to about 15% of one or more emissivity agents taken from thegroup consisting of iron oxide, boron silicide, boron carbide, silicontetraboride, silicon carbide powder, molybdenum disilicide, tungstendisilicide, and zirconium diboride; b. from about 10% to about 30%sodium silicate, from about 50% to about 79% silicon dioxide powder,from about 4% to about 15% of one or more emissivity agents taken fromthe group consisting of iron oxide, boron silicide, boron carbide,silicon tetraboride, silicon carbide powder, molybdenum disilicide,tungsten disilicide, and zirconium diboride, and from about 1% to about5% of a stabilizer taken from the group consisting of bentonite, kaolin,magnesium alumina silica clay, tabular alumina, and stabilized zirconiumoxide; c. from about 10% to about 30% colloidal silica, from about 50%to about 79% silicon dioxide powder, and from about 2% to about 15% ofone or more emissivity agents taken from the group consisting of ironoxide, boron silicide, boron carbide, silicon tetraboride, siliconcarbide molybdenum disilicide, tungsten disilicide, and zirconiumdiboride; or d. from about 10% to about 30% colloidal silica, from about50% to about 79% silicon dioxide powder, from about 2% to about 15% ofone or more essivity agents taken from the group consisting of ironoxide, boron silicide, boron carbide, silicon tetraboride, siliconcarbide molybdenum disilicide, tungsten disilicide, and zirconiumdiboride, and from about 1.5% to about 5.0% of a stabilizer taken fromthe group consisting of bentonite, kaolin, magnesium alumina silicaclay, tabular alumina, and stabilized zirconium oxide.
 10. The processof claim 2, wherein: a second thermal process tube is provided about thefirst thermal process tube encompassing the first thermal process tubetherein the thermal process tube having first and second ends, whereinthe second end is closed; such that a fluid entering through the firstend of the first thermal tube is ejected out of an opening disposeadjacent the first end of the second thermal tube.
 11. A process ofmanufacturing vinyl chloride monomers, comprising: cracking an ethylenedichloride feedstock in a pyrolysis furnace by feeding the feedstockthrough at least one heated process tube having first and second ends,the pyrolysis furnace comprises a firebox chamber having refractorywalls with exposed surfaces, and a plurality of heat generating burners;and the at least one process tubes are disposed in a process tubestructure within the firebox chamber, and in fluid communicationtherethrough, permitting the feedstock to pass through the fireboxchamber while fluidly contained solely within the process tubestructure, and an external surface directly exposed to heat generatedwithin the firebox chamber for thermal communication therethroughwherein a thermal protective layer consisting of a high emissivitycoating is disposed on the internal surface, the external surface of theprocess tubes, the exposed surfaces of the refractory walls, orcombinations thereof, wherein the thermal protective layer contains a.from about 5% to about 30% of an inorganic adhesive, from about 45% toabout 92% of a filler, and from about 1% to about 20% of one or moreemissivity agents, or b. from about 5% to about 35% of colloidal silica,colloidal alumina, or combinations thereof; from about 23% to about 79%of a filler, ftom about 1% to about 20% of one or more emissivityagents.
 12. The process of claim 11, wherein: the thermal protectivelayer further comprises from about 1.0% to about 5.0% of a stabilizer;the thermal protective layer further comprises a surfactant; the thermalprotective layer further comprises a colorant; the inorganic adhesive istaken from the group consisting of an alkali/alkaline earth metalsilicate taken from the group consisting of sodium silicate, potassiumsilicate, calcium silicate, and magnesium silicate; the filler is takenfrom the group consisting of silicon dioxide, aluminum oxide, titaniumdioxide, magnesium oxide, calcium oxide, and boron oxide; the one ormore emissivity agents are taken from the group consisting of siliconhexaboride, boron carbide, silicon tetraboride, silicon carbide,molybdenum disilicide, tungsten disilicide, zirconium diboride, cupricchromite, and metallic oxides; or combinations thereof; the stabilizeris taken from the group consisting of bentonite, kaolin, magnesiumalumna silica clay, tabular alumina, and stabilized zirconium oxide; thethermal protective layer is from about two (2) mils (about 50 microns(μ)) to about ten (10) mils (about 255μ) thick; or combinations thereof.13. The process of claim 11, wherein: a thermal protective layercontains a. from about 5% to about 30% of an inorganic adhesive, theinorganic adhesive is taken from the group consisting of analkali/alkaline earth metal silicate taken from the group consisting ofsodium silicate, potassium silicate, calcium silicate, and magnesiumsilicate; from about 45% to about 92% of a filler, the filler taken fromthe group consisting of silicon dioxide, aluminum oxide, titaniumdioxide, magnesium oxide, calcium oxide, and boron oxide; and from about1% to about 20% of one or more emissivity agents taken from the groupconsisting of silicon hexaboride, boron carbide, silicon tetraboride,silicon carbide, molybdenum disilicide, tungsten disilicide, zirconiumdiboride, cupric chromite, and metallic oxides; b. from about 5% toabout 35% of colloidal silica, colloidal alumina, or combinationsthereof; from about 23% to about 79% of a filler taken from the groupconsisting of silicon dioxide, aluminum oxide, titanium dioxide,magnesium oxide, calcium oxide, and boron oxide; and from about 1% toabout 20% of one or more emissivity agents taken from the groupconsisting of silicon hexaboride, boron carbide, silicon tetraboride,silicon carbide, molybdenum disilicide, tungsten disilicide, zirconiumdiboride, cupric chromite, and metallic oxides; c. from about 5% toabout 30% of an inorganic adhesive, the inorganic adhesive is taken fromthe group consisting of an alkali/alkaline earth metal silicate takenfrom the group consisting of sodium silicate, potassium silicate,calcium silicate, and magnesium silicate; from about 45% to about 92% ofa filler, the filler taken from the group consisting of silicon dioxide,aluminum oxide, titanium dioxide, magnesium oxide, calcium oxide, andboron oxide; and from about 1% to about 20% of one or more emissivityagents taken from the group consisting of silicon hexaboride, boroncarbide, silicon tetraboride, silicon carbide, molybdenum disilicide,tungsten disilicide, zirconium diboride, cupric chromite, and metallicoxides; and from about 1% to about 5% of a stabilizer taken from thegroup consisting of bentonite, kaolin, magnesium alumina silica clay,tabular alumina, and stabilized zirconium oxide; or d. from about 5% toabout 35% of colloidal silica, colloidal alumina, or combinationsthereof; from about 23% to about 79% of a filler taken from the groupconsisting of silicon dioxide, aluminum oxide, titanium dioxide,magnesium oxide, calcium oxide, and boron oxide; and from about 1% toabout 20% of one or more emissivity agents taken from the groupconsisting of silicon hexaboride, boron carbide, silicon tetraboride,silicon carbide, molybdenum disilicide, tungsten disilicide, zirconiumdiboride, cupric chromite, and metallic oxides; and from about 1.5% toabout 5.0% of a stabilizer taken from the group consisting of bentonite,kaolin, magnesium alumina silica clay, tabular alumina, and stabilizedzirconium oxide.
 14. The process of claim 11, wherein: a thermalprotective layer contains a. from about 10% to about 30% sodiumsilicate, from about 50% to about 79% silicon dioxide powder, and fromabout 4% to about 15% of one or more emissivity agents taken from thegroup consisting of iron oxide, boron silicide, boron carbide, silicontetraboride, silicon carbide powder, molybdenum disilicide, tungstendisilicide, and zirconium diboride; b. from about 10% to about 30%sodium silicate, from about 50% to about 79% silicon dioxide powder,from about 4% to about 15% of one or more emissivity agents taken fromthe group consisting of iron oxide, boron silicide, boron carbide,silicon tetraboride, silicon carbide powder, molybdenum disilicide,tungsten disilicide, and zirconium diboride, and from about 1% to about5% of a stabilizer taken from the group consisting of bentonite, kaolin,magnesium alumina silica clay, tabular alumina, and stabilized zirconiumoxide; c. from about 10% to about 30% colloidal silica, from about 50%to about 79% silicon dioxide powder, and from about 2% to about 15% ofone or more emissivity agents taken from the group consisting of ironoxide, boron silicide, boron carbide, silicon tetraboride, siliconcarbide molybdenum disilicide, tungsten disilicide, and zirconiumdiboride; or d. from about 10% to about 30% colloidal silica, from about50% to about 79% silicon dioxide powder, from about 2% to about 15% ofone or more emissivity agents taken from the group consisting of ironoxide, boron silicide, boron carbide, silicon tetraboride, siliconcarbide molybdenum disilicide, tungsten disilicide, and zirconiumdiboride, and from about 1.5% to about 5.0% of a stabilizer taken fromthe group consisting of bentonite, kaolin, magnesium alumina silicaclay, tabular alumina, and stabilized zirconium oxide.
 15. The processof claim 11, wherein: a second thermal process tube is provided aboutthe first thermal process tube encompassing the first thermal processtube therein the thermal process tube having first and second ends,wherein the second end is closed; such that a fluid entering through thefirst end of the first thermal tube is ejected out of an opening disposeadjacent the first end of the second thermal tube.
 16. An apparatus forproducing vinyl chloride monomer from ethylene dichloride, comprising: acracking furnace, a quencher, and a fractionator; the cracking furnacehaving a firebox defining a chamber having refractory walls, andcontaining a plurality of heat generating burners disposed within thefirebox chamber, each refractory wall having an internal surface exposedto heat generated by the burners, a process tube structure having atleast one process tube disposed within the firebox chamber, and in fluidcommunication from an inlet for receiving an ethylene dichloridefeedstock through the firebox chamber to the quencher, permitting theethylene dichloride feedstock to pass through the firebox chamber to becracked forming a mixture of products fluidly contained solely withinthe process tube structure, wherein each process tube has an internalsurface defining an interior space, and an external surface directlyexposed to the heat generated within the firebox chamber for thermalcommunication therethrough, each process tube extending from a first endto a second end allowing fluid communication therethrough, means forfeeding the ethylene dichloride feedstock into the process tubestructure through the first end of each process tube wherein the feedstock fluid mixture flows through the interior space of each processtube from first through second ends heated therein by thermalcommunication through the process tube, discharging a cracked productcontaining the fluid mixture of products out of the second end of eachprocess tub, and then out of the firebox chamber into the quencher toform vinyl chloride monomer, at least one thermal protective layerconsisting of a high emissivity coating disposed on the external surfaceof the process tube, on the internal surface of the process tube, or onat least a part of the internal surface of the firebox chamberrefractory wall, or combinations thereof, wherein a thermal protectivelayer contains a. from about 5% to about 30% of an inorganic adhesive,from about 45% to about 92% of a filler, and from about 1% to about 20%of one or more emissivity agents, or b. from about 5% to about 35% ofcolloidal silica, colloidal alumina, or combinations thereof; from about23% to about 79% of a filler, from about 1% to about 20% of one or moreemissivity agents; the quencher is in fluid communication with theoutlet to quench the mixture of products containing vinyl chloridemonomer; and the fractionator is in fluid communication with thequencher to separate the vinyl chloride monomer from the mixture ofproducts.
 17. The apparatus of claim 15, wherein: the fractioilatorfurther separates hydrochloric acid, unreacted ethylene dichloride, orcombinations thereof from the mixture of products and is in fluidcommunication with the means for feeding the ethylene dichloridefeedstock into the process tube structure for recycling.
 18. Theapparatus of claim 15, wherein: the thermal protective layer furthercomprises from about 1.0% to about 5.0% of a stabilizer; the thermalprotective layer further comprises a surfactant; the thermal protectivelayer further comprises a colorant; the inorganic adhesive is taken fromthe group consisting of an alkali/alkaline earth metal silicate takenfrom the group consisting of sodium silicate, potassium silicate,calcium silicate, and magnesium silicate; the filler is taken from thegroup consisting of silicon dioxide, aluminum oxide, titanium dioxide,magnesium oxide, calcium oxide, and boron oxide; the one or moreemissivity agents are taken from the group consisting of siliconhexaboride, boron carbide, silicon tetraboride, silicon carbide,molybdenum disilicide, tungsten disilicide, zirconium diboride, cupricchromite, and metallic oxides; or combinations thereof; the stabilizeris taken from the group consisting of bentonite, kaolin, magnesiumalumina silica clay, tabular alumina, and stabilized zirconium oxide; orcombinations thereof.
 19. The apparatus of claim 15, wherein: a thermalprotective layer contains a. from about 5% to about 30% of an inorganicadhesive, the inorganic adhesive is taken from the group consisting ofan alkalilalkaline earth metal silicate taken from the group consistingof sodium silicate, potassium silicate, calcium silicate, and magnesiumsilicate; from about 45% to about 92% of a filler, the filler taken fromthe group consisting of silicon dioxide, aluminum oxide, titaniumdioxide, magnesium oxide, calcium oxide, and boron oxide; and from about1% to about 20% of one or more emissivity agents taken from the groupconsisting of silicon hexaboride, boron carbide, silicon tetraboride,silicon carbide, molybdenum disilicide, tungsten disilicide, zirconiumdiboride, cupric chromite, and metallic oxides; b. from about 5% toabout 35% of colloidal silica, colloidal alumina, or combinationsthereof; from about 23% to about 79% of a filler taken from the groupconsisting of silicon dioxide, aluminum oxide, titanium dioxide,magnesium oxide, calcium oxide, and boron oxide; and from about 1% toabout 20% of one or more emissivity agents taken from the groupconsisting of silicon hexaboride, boron carbide, silicon tetraboride,silicon carbide, molybdenum disilicide, tungsten disilicide, zirconiumdiboride, cupric chromite, and metallic oxides; c. from about 5% toabout 30% of an inorganic adhesive, the inorganic adhesive is taken fromthe group consisting of an alkali/alkaline earth metal silicate takenfrom the group consisting of sodium silicate, potassium silicate,calcium silicate, and magnesium silicate; from about 45% to about 92% ofa filler, the filler taken from the group consisting of silicon dioxide,aluminum oxide, titanium dioxide, magnesium oxide, calcium oxide, andboron oxide; and from about 1% to about 20% of one or more emissivityagents taken from the group consisting of silicon hexaboride, boroncarbide, silicon tetraboride, silicon carbide, molybdenum disilicide,tungsten disilicide, zirconium diboride, cupric chromite, and metallicoxides; and from about 1% to about 5% of a stabilizer taken from thegroup consisting of bentonite, kaolin, magnesium alumina silica clay,tabular alumina, and stabilized zirconium oxide; or d. from about 5% toabout 35% of colloidal silica, colloidal alumina, or combinationsthereof; from about 23% to about 79% of a filler taken from the groupconsisting of silicon dioxide, aluminum oxide, titanium dioxide,magnesium oxide, calcium oxide, and boron oxide; and from about 1% toabout 20% of one or more emissivity agents taken from the groupconsisting of silicon hexaboride, boron carbide, silicon tetraboride,silicon carbide, molybdenum disilicide, tungsten disilicide, zirconiumdiboride, cupric chromite, and metallic oxides; and from about 1.5% toabout 5.0% of a stabilizer taken from the group consisting of bentonite,kaolin, magnesium alumina silica clay, tabular alumina, and stabilizedzirconium oxide.
 20. The process of claim 15, wherein: a thermalprotective layer contains a. from about 10% to about 30% sodiumsilicate, from about 50% to about 79% silicon dioxide powder, and fromabout 4% to about 15% of one or more emissivity agents taken from thegroup consisting of iron oxide, boron silicide, boron carbide, silicontetraboride, silicon carbide powder, molybdenum disilicide, tungstendisilicide, and zirconium diboride; b. from about 10% to about 30%sodium silicate, from about 50% to about 79% silicon dioxide powder,from about 4% to about 15% of one or more emissivity agents taken fromthe group consisting of iron oxide, boron silicide, boron carbide,silicon tetraboride, silicon carbide powder, molybdenum disilicide,tungsten disilicide, and zirconium diboride, and from about 1% to about5% of a stabilizer taken from the group consisting of bentonite, kaolin,magnesium alumina silica clay, tabular alumina, and stabilized zirconiumoxide; c. from about 10% to about 30% colloidal silica, from about 50%to about 79% silicon dioxide powder, and from about 2% to about 15% ofone or more emissivity agents taken from the group consisting of ironoxide, boron silicide, boron carbide, silicon tetraboride, siliconcarbide molybdenum disilicide, tungsten disilicide, and zirconiumdiboride; or d. from about 10% to about 30% colloidal silica, from about50% to about 79% silicon dioxide powder, from about 2% to about 15% ofone or more emissivity agents taken from the group consisting of ironoxide, boron silicide, boron carbide, silicon tetraboride, siliconcarbide molybdenum disilicide, tungsten disilicide, and zirconiumdiboride, and from about 15% to about 5.0% of a stabilizer taken fromthe group consisting of bentonite, kaolin, magnesium alumina silicaclay, tabular alumina, and stabilized zirconium oxide.
 21. The processof claim 15, wherein: a second thermal process tube is provided aboutthe first thermal process tube encompassing the first thermal processtube therein the thermal process tube having first and second ends,wherein the second end is closed; such that a fluid entering through thefirst end of the first thermal tube is ejected out of an opening disposeadjacent the first end of the second thermal tube.